Estate Sales: I find them interesting for both being able to peruse through (and possibly buy at a discount price) items they once had and to explore the house in question - typically to get new ideas on how to design structures in CAD programs. (When designing structures, I tend to factor livability a bit into the design.)
Normally when I buy stuff from estate sales like this, I show little concern about the value of the items in the (previous) owner's hands. Things change, however, if you as much as know the person who they used to belong to. Mindset switches from 'Oh, it's just another item that I got for a low price at an estate sale', to 'It's something that I got for a low price... which belonged to someone I knew.'
I wonder: If I buy something from such a sale and it has sentimental value to the owner, should I just give it back to them?
Something to think about.